use nu_protocol::{
    ast::{Block, Call, Expr, Expression},
    engine::StateWorkingSet,
    ir::Instruction,
    IntoSpanned, RegId, Type, VarId,
};

use super::{compile_block, compile_expression, BlockBuilder, CompileError, RedirectModes};

/// Compile a call to `if` as a branch-if
pub(crate) fn compile_if(
    working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    // Pseudocode:
    //
    //        %io_reg <- <condition>
    //        not %io_reg
    //        branch-if %io_reg, FALSE
    // TRUE:  ...<true_block>...
    //        jump END
    // FALSE: ...<else_expr>... OR drop %io_reg
    // END:
    let invalid = || CompileError::InvalidKeywordCall {
        keyword: "if".into(),
        span: call.head,
    };

    let condition = call.positional_nth(0).ok_or_else(invalid)?;
    let true_block_arg = call.positional_nth(1).ok_or_else(invalid)?;
    let else_arg = call.positional_nth(2);

    let true_block_id = true_block_arg.as_block().ok_or_else(invalid)?;
    let true_block = working_set.get_block(true_block_id);

    let true_label = builder.label(None);
    let false_label = builder.label(None);
    let end_label = builder.label(None);

    let not_condition_reg = {
        // Compile the condition first
        let condition_reg = builder.next_register()?;
        compile_expression(
            working_set,
            builder,
            condition,
            RedirectModes::value(condition.span),
            None,
            condition_reg,
        )?;

        // Negate the condition - we basically only want to jump if the condition is false
        builder.push(
            Instruction::Not {
                src_dst: condition_reg,
            }
            .into_spanned(call.head),
        )?;

        condition_reg
    };

    // Set up a branch if the condition is false.
    builder.branch_if(not_condition_reg, false_label, call.head)?;
    builder.add_comment("if false");

    // Compile the true case
    builder.set_label(true_label, builder.here())?;
    compile_block(
        working_set,
        builder,
        true_block,
        redirect_modes.clone(),
        Some(io_reg),
        io_reg,
    )?;

    // Add a jump over the false case
    builder.jump(end_label, else_arg.map(|e| e.span).unwrap_or(call.head))?;
    builder.add_comment("end if");

    // On the else side now, assert that io_reg is still valid
    builder.set_label(false_label, builder.here())?;
    builder.mark_register(io_reg)?;

    if let Some(else_arg) = else_arg {
        let Expression {
            expr: Expr::Keyword(else_keyword),
            ..
        } = else_arg
        else {
            return Err(invalid());
        };

        if else_keyword.keyword.as_ref() != b"else" {
            return Err(invalid());
        }

        let else_expr = &else_keyword.expr;

        match &else_expr.expr {
            Expr::Block(block_id) => {
                let false_block = working_set.get_block(*block_id);
                compile_block(
                    working_set,
                    builder,
                    false_block,
                    redirect_modes,
                    Some(io_reg),
                    io_reg,
                )?;
            }
            _ => {
                // The else case supports bare expressions too, not only blocks
                compile_expression(
                    working_set,
                    builder,
                    else_expr,
                    redirect_modes,
                    Some(io_reg),
                    io_reg,
                )?;
            }
        }
    } else {
        // We don't have an else expression/block, so just set io_reg = Empty
        builder.load_empty(io_reg)?;
    }

    // Set the end label
    builder.set_label(end_label, builder.here())?;

    Ok(())
}

/// Compile a call to `match`
pub(crate) fn compile_match(
    working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    // Pseudocode:
    //
    //         %match_reg <- <match_expr>
    //         collect %match_reg
    //         match (pat1), %match_reg, PAT1
    // MATCH2: match (pat2), %match_reg, PAT2
    // FAIL:   drop %io_reg
    //         drop %match_reg
    //         jump END
    // PAT1:   %guard_reg <- <guard_expr>
    //         check-match-guard %guard_reg
    //         not %guard_reg
    //         branch-if %guard_reg, MATCH2
    //         drop %match_reg
    //         <...expr...>
    //         jump END
    // PAT2:   drop %match_reg
    //         <...expr...>
    //         jump END
    // END:
    let invalid = || CompileError::InvalidKeywordCall {
        keyword: "match".into(),
        span: call.head,
    };

    let match_expr = call.positional_nth(0).ok_or_else(invalid)?;

    let match_block_arg = call.positional_nth(1).ok_or_else(invalid)?;
    let match_block = match_block_arg.as_match_block().ok_or_else(invalid)?;

    let match_reg = builder.next_register()?;

    // Evaluate the match expression (patterns will be checked against this).
    compile_expression(
        working_set,
        builder,
        match_expr,
        RedirectModes::value(match_expr.span),
        None,
        match_reg,
    )?;

    // Important to collect it first
    builder.push(Instruction::Collect { src_dst: match_reg }.into_spanned(match_expr.span))?;

    // Generate the `match` instructions. Guards are not used at this stage.
    let mut match_labels = Vec::with_capacity(match_block.len());
    let mut next_labels = Vec::with_capacity(match_block.len());
    let end_label = builder.label(None);

    for (pattern, _) in match_block {
        let match_label = builder.label(None);
        match_labels.push(match_label);
        builder.push(
            Instruction::Match {
                pattern: Box::new(pattern.pattern.clone()),
                src: match_reg,
                index: match_label.0,
            }
            .into_spanned(pattern.span),
        )?;
        // Also add a label for the next match instruction or failure case
        next_labels.push(builder.label(Some(builder.here())));
    }

    // Match fall-through to jump to the end, if no match
    builder.load_empty(io_reg)?;
    builder.drop_reg(match_reg)?;
    builder.jump(end_label, call.head)?;

    // Generate each of the match expressions. Handle guards here, if present.
    for (index, (pattern, expr)) in match_block.iter().enumerate() {
        let match_label = match_labels[index];
        let next_label = next_labels[index];

        // `io_reg` and `match_reg` are still valid at each of these branch targets
        builder.mark_register(io_reg)?;
        builder.mark_register(match_reg)?;

        // Set the original match instruction target here
        builder.set_label(match_label, builder.here())?;

        // Handle guard, if present
        if let Some(guard) = &pattern.guard {
            let guard_reg = builder.next_register()?;
            compile_expression(
                working_set,
                builder,
                guard,
                RedirectModes::value(guard.span),
                None,
                guard_reg,
            )?;
            builder
                .push(Instruction::CheckMatchGuard { src: guard_reg }.into_spanned(guard.span))?;
            builder.push(Instruction::Not { src_dst: guard_reg }.into_spanned(guard.span))?;
            // Branch to the next match instruction if the branch fails to match
            builder.branch_if(
                guard_reg,
                next_label,
                // Span the branch with the next pattern, or the head if this is the end
                match_block
                    .get(index + 1)
                    .map(|b| b.0.span)
                    .unwrap_or(call.head),
            )?;
            builder.add_comment("if match guard false");
        }

        // match_reg no longer needed, successful match
        builder.drop_reg(match_reg)?;

        // Execute match right hand side expression
        if let Some(block_id) = expr.as_block() {
            let block = working_set.get_block(block_id);
            compile_block(
                working_set,
                builder,
                block,
                redirect_modes.clone(),
                Some(io_reg),
                io_reg,
            )?;
        } else {
            compile_expression(
                working_set,
                builder,
                expr,
                redirect_modes.clone(),
                Some(io_reg),
                io_reg,
            )?;
        }

        // Jump to the end after the match logic is done
        builder.jump(end_label, call.head)?;
        builder.add_comment("end match");
    }

    // Set the end destination
    builder.set_label(end_label, builder.here())?;

    Ok(())
}

/// Compile a call to `let` or `mut` (just do store-variable)
pub(crate) fn compile_let(
    working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    _redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    // Pseudocode:
    //
    // %io_reg <- ...<block>... <- %io_reg
    // store-variable $var, %io_reg
    let invalid = || CompileError::InvalidKeywordCall {
        keyword: "let".into(),
        span: call.head,
    };

    let var_decl_arg = call.positional_nth(0).ok_or_else(invalid)?;
    let block_arg = call.positional_nth(1).ok_or_else(invalid)?;

    let var_id = var_decl_arg.as_var().ok_or_else(invalid)?;
    let block_id = block_arg.as_block().ok_or_else(invalid)?;
    let block = working_set.get_block(block_id);

    let variable = working_set.get_variable(var_id);

    compile_block(
        working_set,
        builder,
        block,
        RedirectModes::value(call.head),
        Some(io_reg),
        io_reg,
    )?;

    // If the variable is a glob type variable, we should cast it with GlobFrom
    if variable.ty == Type::Glob {
        builder.push(
            Instruction::GlobFrom {
                src_dst: io_reg,
                no_expand: true,
            }
            .into_spanned(call.head),
        )?;
    }

    builder.push(
        Instruction::StoreVariable {
            var_id,
            src: io_reg,
        }
        .into_spanned(call.head),
    )?;
    builder.add_comment("let");

    // Don't forget to set io_reg to Empty afterward, as that's the result of an assignment
    builder.load_empty(io_reg)?;

    Ok(())
}

/// Compile a call to `try`, setting an error handler over the evaluated block
pub(crate) fn compile_try(
    working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    // Pseudocode (literal block):
    //
    //       on-error-into ERR, %io_reg           // or without
    //       %io_reg <- <...block...> <- %io_reg
    //       write-to-out-dests %io_reg
    //       pop-error-handler
    //       jump END
    // ERR:  clone %err_reg, %io_reg
    //       store-variable $err_var, %err_reg         // or without
    //       %io_reg <- <...catch block...> <- %io_reg // set to empty if no catch block
    // END:
    //
    // with expression that can't be inlined:
    //
    //       %closure_reg <- <catch_expr>
    //       on-error-into ERR, %io_reg
    //       %io_reg <- <...block...> <- %io_reg
    //       write-to-out-dests %io_reg
    //       pop-error-handler
    //       jump END
    // ERR:  clone %err_reg, %io_reg
    //       push-positional %closure_reg
    //       push-positional %err_reg
    //       call "do", %io_reg
    // END:
    let invalid = || CompileError::InvalidKeywordCall {
        keyword: "try".into(),
        span: call.head,
    };

    let block_arg = call.positional_nth(0).ok_or_else(invalid)?;
    let block_id = block_arg.as_block().ok_or_else(invalid)?;
    let block = working_set.get_block(block_id);

    let catch_expr = match call.positional_nth(1) {
        Some(kw_expr) => Some(kw_expr.as_keyword().ok_or_else(invalid)?),
        None => None,
    };
    let catch_span = catch_expr.map(|e| e.span).unwrap_or(call.head);

    let err_label = builder.label(None);
    let end_label = builder.label(None);

    // We have two ways of executing `catch`: if it was provided as a literal, we can inline it.
    // Otherwise, we have to evaluate the expression and keep it as a register, and then call `do`.
    enum CatchType<'a> {
        Block {
            block: &'a Block,
            var_id: Option<VarId>,
        },
        Closure {
            closure_reg: RegId,
        },
    }

    let catch_type = catch_expr
        .map(|catch_expr| match catch_expr.as_block() {
            Some(block_id) => {
                let block = working_set.get_block(block_id);
                let var_id = block.signature.get_positional(0).and_then(|v| v.var_id);
                Ok(CatchType::Block { block, var_id })
            }
            None => {
                // We have to compile the catch_expr and use it as a closure
                let closure_reg = builder.next_register()?;
                compile_expression(
                    working_set,
                    builder,
                    catch_expr,
                    RedirectModes::value(catch_expr.span),
                    None,
                    closure_reg,
                )?;
                Ok(CatchType::Closure { closure_reg })
            }
        })
        .transpose()?;

    // Put the error handler instruction. If we have a catch expression then we should capture the
    // error.
    if catch_type.is_some() {
        builder.push(
            Instruction::OnErrorInto {
                index: err_label.0,
                dst: io_reg,
            }
            .into_spanned(call.head),
        )?
    } else {
        // Otherwise, we don't need the error value.
        builder.push(Instruction::OnError { index: err_label.0 }.into_spanned(call.head))?
    };

    builder.add_comment("try");

    // Compile the block
    compile_block(
        working_set,
        builder,
        block,
        redirect_modes.clone(),
        Some(io_reg),
        io_reg,
    )?;

    // Successful case:
    // - write to the current output destinations
    // - pop the error handler
    if let Some(mode) = redirect_modes.out {
        builder.push(mode.map(|mode| Instruction::RedirectOut { mode }))?;
    }

    if let Some(mode) = redirect_modes.err {
        builder.push(mode.map(|mode| Instruction::RedirectErr { mode }))?;
    }
    builder.push(Instruction::DrainIfEnd { src: io_reg }.into_spanned(call.head))?;
    builder.push(Instruction::PopErrorHandler.into_spanned(call.head))?;

    // Jump over the failure case
    builder.jump(end_label, catch_span)?;

    // This is the error handler
    builder.set_label(err_label, builder.here())?;

    // Mark out register as likely not clean - state in error handler is not well defined
    builder.mark_register(io_reg)?;

    // Now compile whatever is necessary for the error handler
    match catch_type {
        Some(CatchType::Block { block, var_id }) => {
            // Error will be in io_reg
            builder.mark_register(io_reg)?;
            if let Some(var_id) = var_id {
                // Take a copy of the error as $err, since it will also be input
                let err_reg = builder.next_register()?;
                builder.push(
                    Instruction::Clone {
                        dst: err_reg,
                        src: io_reg,
                    }
                    .into_spanned(catch_span),
                )?;
                builder.push(
                    Instruction::StoreVariable {
                        var_id,
                        src: err_reg,
                    }
                    .into_spanned(catch_span),
                )?;
            }
            // Compile the block, now that the variable is set
            compile_block(
                working_set,
                builder,
                block,
                redirect_modes,
                Some(io_reg),
                io_reg,
            )?;
        }
        Some(CatchType::Closure { closure_reg }) => {
            // We should call `do`. Error will be in io_reg
            let do_decl_id = working_set.find_decl(b"do").ok_or_else(|| {
                CompileError::MissingRequiredDeclaration {
                    decl_name: "do".into(),
                    span: call.head,
                }
            })?;

            // Take a copy of io_reg, because we pass it both as an argument and input
            builder.mark_register(io_reg)?;
            let err_reg = builder.next_register()?;
            builder.push(
                Instruction::Clone {
                    dst: err_reg,
                    src: io_reg,
                }
                .into_spanned(catch_span),
            )?;

            // Push the closure and the error
            builder
                .push(Instruction::PushPositional { src: closure_reg }.into_spanned(catch_span))?;
            builder.push(Instruction::PushPositional { src: err_reg }.into_spanned(catch_span))?;

            // Call `$err | do $closure $err`
            builder.push(
                Instruction::Call {
                    decl_id: do_decl_id,
                    src_dst: io_reg,
                }
                .into_spanned(catch_span),
            )?;
        }
        None => {
            // Just set out to empty.
            builder.load_empty(io_reg)?;
        }
    }

    // This is the end - if we succeeded, should jump here
    builder.set_label(end_label, builder.here())?;

    Ok(())
}

/// Compile a call to `loop` (via `jump`)
pub(crate) fn compile_loop(
    working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    _redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    // Pseudocode:
    //
    //       drop %io_reg
    // LOOP: %io_reg <- ...<block>...
    //       drain %io_reg
    //       jump %LOOP
    // END:  drop %io_reg
    let invalid = || CompileError::InvalidKeywordCall {
        keyword: "loop".into(),
        span: call.head,
    };

    let block_arg = call.positional_nth(0).ok_or_else(invalid)?;
    let block_id = block_arg.as_block().ok_or_else(invalid)?;
    let block = working_set.get_block(block_id);

    let loop_ = builder.begin_loop();
    builder.load_empty(io_reg)?;

    builder.set_label(loop_.continue_label, builder.here())?;

    compile_block(
        working_set,
        builder,
        block,
        RedirectModes::default(),
        None,
        io_reg,
    )?;

    // Drain the output, just like for a semicolon
    builder.drain(io_reg, call.head)?;

    builder.jump(loop_.continue_label, call.head)?;
    builder.add_comment("loop");

    builder.set_label(loop_.break_label, builder.here())?;
    builder.end_loop(loop_)?;

    // State of %io_reg is not necessarily well defined here due to control flow, so make sure it's
    // empty.
    builder.mark_register(io_reg)?;
    builder.load_empty(io_reg)?;

    Ok(())
}

/// Compile a call to `while`, via branch instructions
pub(crate) fn compile_while(
    working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    _redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    // Pseudocode:
    //
    // LOOP:  %io_reg <- <condition>
    //        branch-if %io_reg, TRUE
    //        jump FALSE
    // TRUE:  %io_reg <- ...<block>...
    //        drain %io_reg
    //        jump LOOP
    // FALSE: drop %io_reg
    let invalid = || CompileError::InvalidKeywordCall {
        keyword: "while".into(),
        span: call.head,
    };

    let cond_arg = call.positional_nth(0).ok_or_else(invalid)?;
    let block_arg = call.positional_nth(1).ok_or_else(invalid)?;
    let block_id = block_arg.as_block().ok_or_else(invalid)?;
    let block = working_set.get_block(block_id);

    let loop_ = builder.begin_loop();
    builder.set_label(loop_.continue_label, builder.here())?;

    let true_label = builder.label(None);

    compile_expression(
        working_set,
        builder,
        cond_arg,
        RedirectModes::value(call.head),
        None,
        io_reg,
    )?;

    builder.branch_if(io_reg, true_label, call.head)?;
    builder.add_comment("while");
    builder.jump(loop_.break_label, call.head)?;
    builder.add_comment("end while");

    builder.set_label(true_label, builder.here())?;

    compile_block(
        working_set,
        builder,
        block,
        RedirectModes::default(),
        None,
        io_reg,
    )?;

    // Drain the result, just like for a semicolon
    builder.drain(io_reg, call.head)?;

    builder.jump(loop_.continue_label, call.head)?;
    builder.add_comment("while");

    builder.set_label(loop_.break_label, builder.here())?;
    builder.end_loop(loop_)?;

    // State of %io_reg is not necessarily well defined here due to control flow, so make sure it's
    // empty.
    builder.mark_register(io_reg)?;
    builder.load_empty(io_reg)?;

    Ok(())
}

/// Compile a call to `for` (via `iterate`)
pub(crate) fn compile_for(
    working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    _redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    // Pseudocode:
    //
    //       %stream_reg <- <in_expr>
    // LOOP: iterate %io_reg, %stream_reg, END
    //       store-variable $var, %io_reg
    //       %io_reg <- <...block...>
    //       drain %io_reg
    //       jump LOOP
    // END:  drop %io_reg
    let invalid = || CompileError::InvalidKeywordCall {
        keyword: "for".into(),
        span: call.head,
    };

    if call.get_named_arg("numbered").is_some() {
        // This is deprecated and we don't support it.
        return Err(invalid());
    }

    let var_decl_arg = call.positional_nth(0).ok_or_else(invalid)?;
    let var_id = var_decl_arg.as_var().ok_or_else(invalid)?;

    let in_arg = call.positional_nth(1).ok_or_else(invalid)?;
    let in_expr = in_arg.as_keyword().ok_or_else(invalid)?;

    let block_arg = call.positional_nth(2).ok_or_else(invalid)?;
    let block_id = block_arg.as_block().ok_or_else(invalid)?;
    let block = working_set.get_block(block_id);

    // Ensure io_reg is marked so we don't use it
    builder.mark_register(io_reg)?;

    let stream_reg = builder.next_register()?;

    compile_expression(
        working_set,
        builder,
        in_expr,
        RedirectModes::value(in_expr.span),
        None,
        stream_reg,
    )?;

    // Set up loop state
    let loop_ = builder.begin_loop();
    builder.set_label(loop_.continue_label, builder.here())?;

    // This gets a value from the stream each time it's executed
    // io_reg basically will act as our scratch register here
    builder.push(
        Instruction::Iterate {
            dst: io_reg,
            stream: stream_reg,
            end_index: loop_.break_label.0,
        }
        .into_spanned(call.head),
    )?;
    builder.add_comment("for");

    // Put the received value in the variable
    builder.push(
        Instruction::StoreVariable {
            var_id,
            src: io_reg,
        }
        .into_spanned(var_decl_arg.span),
    )?;

    // Do the body of the block
    compile_block(
        working_set,
        builder,
        block,
        RedirectModes::default(),
        None,
        io_reg,
    )?;

    // Drain the output, just like for a semicolon
    builder.drain(io_reg, call.head)?;

    // Loop back to iterate to get the next value
    builder.jump(loop_.continue_label, call.head)?;

    // Set the end of the loop
    builder.set_label(loop_.break_label, builder.here())?;
    builder.end_loop(loop_)?;

    // We don't need stream_reg anymore, after the loop
    // io_reg may or may not be empty, so be sure it is
    builder.free_register(stream_reg)?;
    builder.mark_register(io_reg)?;
    builder.load_empty(io_reg)?;

    Ok(())
}

/// Compile a call to `break`.
pub(crate) fn compile_break(
    _working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    _redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    if builder.is_in_loop() {
        builder.load_empty(io_reg)?;
        builder.push_break(call.head)?;
        builder.add_comment("break");
    } else {
        // Fall back to calling the command if we can't find the loop target statically
        builder.push(
            Instruction::Call {
                decl_id: call.decl_id,
                src_dst: io_reg,
            }
            .into_spanned(call.head),
        )?;
    }
    Ok(())
}

/// Compile a call to `continue`.
pub(crate) fn compile_continue(
    _working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    _redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    if builder.is_in_loop() {
        builder.load_empty(io_reg)?;
        builder.push_continue(call.head)?;
        builder.add_comment("continue");
    } else {
        // Fall back to calling the command if we can't find the loop target statically
        builder.push(
            Instruction::Call {
                decl_id: call.decl_id,
                src_dst: io_reg,
            }
            .into_spanned(call.head),
        )?;
    }
    Ok(())
}

/// Compile a call to `return` as a `return-early` instruction.
///
/// This is not strictly necessary, but it is more efficient.
pub(crate) fn compile_return(
    working_set: &StateWorkingSet,
    builder: &mut BlockBuilder,
    call: &Call,
    _redirect_modes: RedirectModes,
    io_reg: RegId,
) -> Result<(), CompileError> {
    // Pseudocode:
    //
    // %io_reg <- <arg_expr>
    // return-early %io_reg
    if let Some(arg_expr) = call.positional_nth(0) {
        compile_expression(
            working_set,
            builder,
            arg_expr,
            RedirectModes::value(arg_expr.span),
            None,
            io_reg,
        )?;
    } else {
        builder.load_empty(io_reg)?;
    }

    // TODO: It would be nice if this could be `return` instead, but there is a little bit of
    // behaviour remaining that still depends on `ShellError::Return`
    builder.push(Instruction::ReturnEarly { src: io_reg }.into_spanned(call.head))?;

    // io_reg is supposed to remain allocated
    builder.load_empty(io_reg)?;

    Ok(())
}